DE102005014966A1 - Process for producing welded rolling bearing rings from bearing steel - Google Patents

Abstract

Method for producing welded rolling bearing rings from bearing steel, comprising the following steps: DOLLAR A - cold forming a tube from a cold or hot strip, DOLLAR A - longitudinal welding of the tube in a butt welding process, DOLLAR A - removing the Schweißaufwurfs, DOLLAR A - cutting of ring blanks of the Tube, DOLLAR A - Cold rolling of the ring blanks and DOLLAR A - Thermal and / or mechanical reworking of the ring blanks to complete the rolling bearing rings.

Description

Territory of invention

The The invention relates to a method for producing welded rolling bearing rings from bearing steel.

background the invention

The Production of radial roller bearing rings, So of inner and outer rings Ball bearings, needle bearings or roller bearings, is usually carried out by Machining the rolling bearing steel in soft annealed Condition to which a hardness and tempering step as well as finishing by grinding or Honing connects. Alternatively, it is also known, rolling bearing rings by joining technology a wire or strip material, including resistance or slow butt welding process to offer. A load-bearing rolling bearing ring and a corresponding method for producing the same from the unpublished German Patent application 10 2005 014 967.7 of the applicant known. Such a Rolling bearing ring draws through a joint on, the hardness at least the hardness the residual cross-section is, in general, even a little harder, what the extremely fine carbide formation and high carbide number in weld area is due. As a result of this hardness homogeneity and the Circumstance that the weld is no longer the weak point of the ring, are such rolling bearing rings also for higher Load applications suitable.

The at the resistance or Abbremsstumpfschweißigten made seams are provided with a Aufwurf, scraped off by means of profile tools or milled off must become. Is appropriate it with regard to a symmetrical voltage curve, the rings from two segments offset by 180 ° welds manufacture. In general, the production of individual rings in terms of on the high cycle times of 0.5-1.5s with regard to one economic production difficult to master. This is especially true if to attach double welds are. Added to this is the microstructure in the welding zone with structure fractions like ledeburite, ie stem crystals, microsections, high voltages and different structural states. The usual for one such structural condition required Normalisierungsglühvorgänge can due to the production conditions are not specifically carried out. Rather, it is assumed that the structural homogeneity is largely due to austenitization for hardening achieved at temperatures between 820-880 ° C becomes. Furthermore is the technological and human effort involved in manufacturing individual rings connected in this way is considerable.

Under consideration the fact that rolling bearing rings made in this way do not have the same good rolling properties may have due to the one or the two given welds are such rings basically to classify as less resilient than rings of seamless starting material. For many Applications, however, this is a completely sufficient condition.

Summary the invention

Of the The invention is based on the problem of specifying a method which in a simple and efficient way the production of rolling bearing rings allows.

• – Kaltverformen eines Rohres aus einem Kalt- oder Warmband,
• – Längsschweißen des Rohres in einem Stumpfschweißverfahren,
• – Entfernen des Schweißaufwurfs,
• – Ablängen von Ringrohlingen von dem Rohr,
• – Kaltwalzen der Ringrohlinge, und
• – thermische und/oder mechanische Nachbearbeitung der Ringrohlinge zur Fertigstellung der Wälzlagerringe.

To solve this problem, the following steps are provided in a method for producing welded bearing rings from rolling bearing steel:

• Cold forming of a tube from a cold or hot strip,
• Longitudinal welding of the tube in a butt-welding process,
• - removal of the Schweißaufwurfs,
• Cutting of ring blanks from the pipe,
• - Cold rolling of the ring blanks, and
• - Thermal and / or mechanical post-processing of the ring blanks for completing the rolling bearing rings.

The inventive method proposes a two-stage manufacturing process, that is, the cold deformation and welding of a tube for the ring blanks takes place separately before the actual production of the individual rolling bearing rings. Thus, a process-safe, practicable in practice production with little human and technological effort is possible. The first step is to achieve and maintain a weld seam factor approaching 1, which can be achieved primarily with the choice of the appropriate material in conjunction with the appropriate joining technique and heat treatment. After a pipe according to the invention is first produced in a welding step, much better homogenous weld seam properties can be necessarily achieved than would be the case with individual welds of the individual rings. According to generally accepted rules, metals and alloys with a defined melting temperature are considered weldable, which is why even steels with higher carbon and alloy contents are basically weldable. The choice of the material used in connection with the welding process, ie z. B. the resistance Butt welding, allows the use of a steel material with a carbon content of z. B. 0.35-0.55% and other elements that are listed by way of example below. For fine grain stabilization, an aluminum content of 0.015-0.060% is suggested, alternatively also niobium in the range of 20-80 ppm, alternatively boron as an element for fine grain formation, but also for increasing the hardenability and toughness.

A usable steel alloy includes, for example, the following elements: Carbon: 0.35-0.55% Silicon max .: 0.25% Manganese: 0.50 to 0.90% Phosphorus max .: 0.020% Sulfur max: 0.005% Aluminum: 0.015 to 0.050% Chrome max .: 0.15% Nickel max .: 0.25% Copper max .: 0.25% Rest iron.

Further Elements such as tin, antimony and selenium are as common for steel limited above.

The conversion behavior resulting from this material composition in the ZTU chart and the calculated hardenability allows the Ver equal to previously known material properties known Materials.

in the first method step according to the invention will now be first a cold or hot strip welded to a tube. A band with a thickness tolerance of ≤ 2%, in particular ≤ 1%, is used, which is especially advantageous with regard to the ultimately resulting wall thickness tolerance the produced rolling bearing rings is, depending on the used tape just a corresponding thickness tolerance exhibit. The width of the tape used is analogous to the later diameter calculated below taking into account the sweat addition. This band is now continuously cold-formed to the tube and by means of Resistance or induction heating and longitudinally welded according to the corresponding compression pressure. The welding temperature lies in the range between the solidus and the liquidus line of the used steel. The joining pressure takes care of a defect-free joint, excess material is pressed out of the seam in the doughy state. The resulting bulges, inside and outside, by suitable Cutting tools continuously processed. The cold strip is preferably in an endless process converted to an endless tube, the in a continuous welding process is welded, after completion of the continuous tube individual tubes with a length of 1-10 m, especially from 3-8 m cut to length become.

During the joining process it comes to considerable tensions, due to the temperature profile and the transformation. On cooling from this sweat heat it now requires special measures to suppress the formation of martensite and the welding stresses and to keep the shrinkage stresses low. This is done appropriately in that preferably immediately after the joint rewarming means Induction to a temperature below the AC1 temperature and above the martensite start temperature of the rolling bearing steel takes place. Prefers Here is a temperature interval between 320 ° C-440 ° C, preferably 340 ° C-420 ° C. hereby Is it possible, even below the scale limit, the oxidation of the surface is low to keep or avoid.

at This so-called "endless production" is also created in the product length considerable tension, which can build up significantly due to the length and lead to cross cracks can. To eliminate these is still proposed, according to welding, especially after reheating, a stress relief annealing with subsequent targeted cooling, in particular with a cooling rate from 30 ° C-70 ° C per minute, preferably at 50 ° C per minute, to perform. This stress relief annealer takes place for example at a distance of 1-2 m from the joining station removed, so after cooling another warming is achieved and a slow cooling is achieved. this happens preferably in a ring-like inductor combined with a cooling fan.

At It should be noted that this rewarming or the stress relief annealing also at the cut from the endless tube Single tubes can be made, if appropriate.

As described, an endless tube is preferably produced, which is cut to a length of, for example, 3-8 m. After cutting to length, normalization annealing preferably follows, in particular at a temperature between 880 ° C.-920 ° C. During this Normalisierungsglühung the weld structure structures are converted to the normal state of the basic structure and reduced voltages. After Normalisierungsglühung there is a prefabricated tube or a so-called tube billet, which has a typical dimension of 50 mm outer diameter and 5 mm wall thickness. The wall thickness tolerance of the pipe corresponds to that of the used cold or hot strip. In other words, the smaller the strip thickness tolerance, the lower, of course, is the thickness tolerance of the front pipe. Thus, if the cold or hot strip has a thickness tolerance of ± 1%, then the front tube has a thickness tolerance of ± 1%, in contrast to a seamless tube, which has a best possible wall thickness tolerance of ± 5%.

To Normalizing the Vorrohr is preferably cooled under inert gas, the Surface cleaned and prepared for subsequent cold drawing, including appropriate Drawing agents, as they are known in the art, are to be selected. The following Cold drawing in the normalized state is possible after the pre-pipe a fine-grained pearlite structure having. The degree of cold working should be between 5% -15%, in particular at about 10%, are. The cold-drawn tube has an extraordinary high dimensional and dimensional accuracy, about the cold drawing step can provide the required wall thickness as needed be stripped.

to Refinement of further processing, it is possible after cold drawing a recrystallization annealing, in particular at a temperature between 630 ° C-750 ° C, preferably from 650 ° C-720 ° C, in particular at a holding time between 0.5h-5h, preferably from 1h-4h to perform. To In this treatment, the tube has a largely molded Structural state, this means not streaky, but grainy Cementite (so-called GKZ structure). This microstructure is as you know, ideally suited for the further soft machining in the form of cold forming.

ever after whether the recrystallization annealing was performed or not, are two different initial structure of the tube before, namely the a normalized structure with a hardness between 300-400 HB and the normalized and recrystallization annealed microstructure in the GKZ state and possibly a calibration strain with a hardness between 160-220 HB, suitable for cal control.

• 1. Die Schweißnaht ist normalisiert, also homogenisiert.
• 2. Die Nahtfestigkeit entspricht annähernd dem Faktor 1 nach den üblichen Regeln der Schweißtechnik.
• 3. Die Oberfläche des Rohres ist nicht entkohlt oder sogar kohlenstoffangereichert auf z. B. 0,6% Rand-Kohlenstoffgehalt mit einer Tiefe bis zu 20% des Rohrquerschnitts.
• 4. Die Wanddickenhomogenität beträgt durch die Verwendung eines Ausgangsbandes mit einer Dickentoleranz von bevorzugt ± 1% ebenfalls nur ca. 1% und erlaubt völlig neue Fertigungsmethoden in der Weiterverarbeitung, da übliche nahtlose Rohre einen Wanddickenschlag von ± 5% aufweisen.

The tube produced in this way has particular advantages for the rolling bearing ring production that follows, and thus differs considerably from the previously known methods:

• 1. The weld is normalized, so homogenized.
• 2. The seam strength corresponds to approximately the factor 1 according to the usual rules of welding technology.
• 3. The surface of the tube is not decarburized or even carbon enriched to z. B. 0.6% edge carbon content with a depth up to 20% of the pipe cross-section.
• 4. The wall thickness homogeneity is also only about 1% due to the use of an output strip with a thickness tolerance of preferably ± 1% and allows completely new production methods in further processing since standard seamless tubes have a wall thickness of ± 5%.

To the manufacture of the structural and hard-optimized Pipe takes place in the second stage, the ring production. The ring blanks are cut to length and cold rolled. Since the tube has no decarburization and more surface defects only within the roughness of about 6 microns are present, is a substantial Minimization of machining allowances possible.

The so shaped ring blanks can now after cutting to length, optionally after cold rolling, martensitic hardened and If necessary, be tempered, resulting in a neutral or light carburizing atmosphere can be done. The compressive stresses move at a height of approx. 200 MPa due to slightly carburizing conditions.

To the hardening, optionally after tempering, the ring blanks become mechanical smoothed or honed. The grinding allowances are minimized or are no longer required because the rings have excellent wall homogeneity. It is sufficient consequently only a honing of the raceways or a mechanical one smoothing after curing, there quasi wall thickness equality exists.

If another method of heating chosen is, such. B. inductive heating for surface hardening, arise extraordinarily high hardness values and high compressive stresses due to the additional carburizing and the Kind of deterrence. The residual compressive stresses then reach values above 350 MPa after starting. In particular, the tube from the lamellar State leads out to an excellent surface hardness and a fine-grained martensite with 5-8% Retained austenite and with a carburization of 10-20%.

The Rings have high cycle fatigue life as they do otherwise known only from seamless pipes and blanks. The tenacity of such Rings are twice as high as rings made of 100Cr6, for example H + A.

Of the welding factor from approximate or equal to 1 allows a homogeneous view of the strength properties in static and dynamic cycle bending fatigue strength and the overroll properties.

The rolling bearing rings have excellent hardness properties after curing. In the core range, values of 54-59 HRC and in the edge zone of 60-64 HRC are achieved, whereby these values also occur in the weld seam area. If a surface hardening is carried out, the hardness in the core range is 160-400 HB, depending on the choice of microstructure state, and in the edge zone more than 62 HRC, furthermore high compressive residual stresses over 350 MPa and retained austenite up to 20%.

The Use of such rings is possible in most cases, eg. B. in home appliances, hobby equipment or Water pump outer rings. specially in this latter application, the rings in a aluminum casing pressed, so are not subject to any circumferential rolling load. For standing outer rings and / or medium loads is those with the inventive method achievable ring quality a contribution to the optimization of cost-performance ratios.

Next the method further relates to a welded rolling bearing ring, prepared according to the method described above.

One such rolling bearing ring characterized by a surface hardness of at least 700 HV, with one from the normalization state with very fine cured carbon content roller bearing ring after starting at least 740 HV. The residual toughness the rolling bearing ring according to the invention is at least 1.5% elongation at break. The edge hardening depth is at least 50% of the remaining cross section. If a surface hardening is carried out, then can high hardness values over 62 HRC at the edge with a core hardness above 54 HRC in conjunction with the existing edge carburization and the high core carbon content be achieved.

description the drawing

The single figure shows a flow chart in which the essential steps the method according to the invention again clearly arranged are shown.

Claims (16)

Process for producing welded rolling bearing rings from bearing steel, with the following steps: - cold forming a tube made of a cold or hot strip, - longitudinal welding of the Tube in a butt-welding process, - Remove the sweat release, - Cutting to length Ring blanks from the pipe, - cold rolling of the ring blanks, and - thermal and / or mechanical post-processing of the ring blanks for completion the rolling bearing rings. Method according to claim 1, characterized in that that a cold-rolled strip with a thickness tolerance ≤ 2%, in particular ≤ 1% used becomes. Method according to claim 1 or 2, characterized that the cold strip is formed into an endless tube in a continuous process This is done in a continuous welding process welded is, from which endless tube individual tubes with a length of 1-10 m, especially from 3-8 m cut to length become. Method according to claim 3, characterized that after cutting to length a Normalisierungsglühung especially at a temperature between 880 ° C-920 ° C, takes place. Method according to one of the preceding claims, characterized characterized in that after welding, and optionally before the cutting of the Endless tube, a reheating to a temperature below the AC1 temperature and above the Martensite starting temperature of the rolling bearing steel, in particular to a temperature between 320 ° C-440 ° C, preferably 340 ° C-420 ° C, takes place. Method according to one of the preceding claims, characterized characterized in that after welding, and optionally before the length of the Endlosrohr, in particular after reheating a stress relief annealing with subsequent targeted cooling, in particular with a cooling rate from 30 ° C-70 ° C per minute, preferably with 50 ° C per minute. Method according to one of the preceding claims, characterized characterized in that the tube is cold drawn before cutting the ring blanks, wherein the degree of cold working is between 5% -15%, in particular 10%. Method according to claim 7, characterized in that that after cold drawing a recrystallization annealing, in particular at a temperature between 630 ° C-750 ° C, preferably 650 ° C-720 ° C, in particular takes place at a holding time between 0.5h-5h, preferably 1h-4h. Method according to one of the preceding claims, characterized in that the ring blanks are cold-rolled after being cut to length become. Method according to one of the preceding claims, characterized characterized in that the ring blanks after cutting to length, optionally Hardened martensite after cold rolling and tempered if necessary become. Method according to claim 10, characterized in that that tempering takes place in a neutral or carburizing atmosphere. A method according to claim 10 or 11, characterized in that the ring blanks after the hardening, optionally after tempering mechanically smoothed or honed. welded Roller bearing ring, prepared according to the method of any one of claims 1 to 12. roller bearing ring according to claim 13, characterized in that the surface hardness at least 700 HV, with one of the normalization state with finely divided Carbon hardened rolling bearing ring after tempering is at least 740 HV. roller bearing ring according to claim 13 or 14, characterized in that it has a residual toughness of has at least 1.5% elongation at break. rolling bearing ring according to one of the claims 13 to 15, characterized in that the edge hardening depth at least 50% of the residual cross section.